The present invention relates to a seal between upper and lower halves of an inner compressor discharge case and particularly to a seal between the case halves tolerant of warpage during turbine operation and methods of locating the seal in sealing position in situ.
In a turbine, e.g., a gas turbine, the compressor section includes a stationary inner barrel formed of two semi-cylindrical halves secured one to the other generally along a horizontal midline forming an annulus. The aft end of the inner barrel is secured to a compressor discharge casing which provides support for the nozzle support ring supporting the first-stage nozzle. The inner barrel, in part, segregates a high-pressure region external to the barrel from a lower pressure region within the barrel and about the rotor. The barrel halves at the horizontal midline have metal-to-metal contact surfaces which are machined to high tolerances in efforts to eliminate leakage after assembly and during use. However, warpage during operation of the turbine due to creep can leave a gap of approximately 5 to 7 mils at the bolted horizontal joints between the upper and lower halves of the inner barrel. As a consequence, leakage paths can and do appear between the halves of the inner barrel. A need has therefore arisen to minimize or eliminate any such leakage paths in a manner which is tolerant to warpage during turbine operation.
In accordance with a preferred embodiment of the present invention, there is provided a seal for application along the registering and joined horizontal margins of the halves of the inner compressor discharge case, i.e., the inner barrel, in a manner tolerant to warpage of the inner barrel during turbine operation. Particularly, grooves are machined along the mating margins of the upper and lower barrel halves and between the bolts at axially opposite ends of the inner barrel. The grooves in the margins of the upper barrel half are machined to a depth greater than the depth of the grooves formed along the margins of the lower barrel half. An elongated seal is provided in the registering grooves for sealing engagement along surfaces of the grooves in the opposite barrel halves.
Each elongated seal along each joint includes an elongated metal shim overlaid on opposite sides with a woven metallic cloth and secured to the shims, preferably by welding. Opposite elongated edges of the shim project respectively above and below the area of the shim covered by the metallic cloth. Each edge is formed to project radially inwardly of the inner face of the seal and has a reversely formed arcuate flange. With the seal extending lengthwise in the registering grooves, and the turbine in operation, the arcuate flange of the lower edge of the seal bears and seals against the base of the lower groove. The edge of the upper margin of the shim at the juncture of the arcuate flange and the main body of the shim bears and seals against the innermost wall of the upper groove. It will be appreciated that in the event a gap appears at the joint between the upper and lower barrel halves, the higher pressure external to the inner barrel forces the seal radially inwardly, maintaining the sealing engagement of the upper edge of each shim against the innermost side surface of the upper groove.
In order to locate the shim in sealing location within the groove, the distance, i.e., the depth between the upper and lower arcuate flanges of the seal, is short of or less than the distance between the bases of the registering grooves. More particularly, the depth of the seal approximates the depth of the upper groove. During assembly, the seal is maintained in the upper groove by an adherent material. For example, a wax material may be employed to adhere the seal within the upper groove without any portion of the seal projecting beyond the upper groove. When the upper and lower barrel halves are brought together and bolted, the seal is maintained in the upper groove and does not interfere with the sealing faces of the upper and lower halves.
In order to position the seal in its sealing location spanning between the joint and engaging the sealing surfaces of both grooves, the adherent material loses its adherent character at operating temperatures above ambient and at or below turbine operating temperatures. Consequently, at those temperatures, the seal is enabled to drop into the lower groove under the influence of gravity and thus span across the gap between the upper and lower barrel halves. In the event of a leakage gap between the upper and lower halves during operation, the higher pressure external of the barrel urges the seal radially inwardly to engage the sealing surface of the upper groove while the lower flange of the seal engages and seals against the base of the lower groove.
In a preferred embodiment according to the present invention, there is provided an inner compressor discharge case for a gas turbine, comprising a cylindrical barrel formed of upper and lower halves joined to one another at margins thereof along a horizontal midline to form a pair of diametrically spaced joints along opposite sides of the barrel, each of the margins having a groove extending generally parallel to an axis of the cylindrical barrel, the grooves of opposed margins of the halves on respective opposite sides of the barrel lying in registration with one another along the horizontal midline, a seal disposed in each pair of registering grooves, each seal including a shim having a pair of sealing surfaces for sealing against surfaces of the registering grooves, respectively, and a metallic cloth secured along at least one side of the shim and between the sealing surfaces thereof.
In a further preferred embodiment according to the present invention, there is provided an inner compressor discharge case for a gas turbine, comprising a cylindrical barrel formed of upper and lower halves joined to one another at margins thereof along a horizontal midline to form a pair of diametrically spaced joints along opposite sides of the barrel, each of the margins having a groove extending generally parallel to an axis of the cylindrical barrel, the grooves of opposed margins of the halves on respective opposite sides of the barrel lying in registration with one another along the horizontal midline and a seal disposed in each pair of registering grooves, each seal including a metal plate having a pair of sealing surfaces for sealing against surfaces of the registering grooves, respectively, one of the sealing surfaces including an edge of the plate extending out of a plane containing the plate for sealing against a surface of one of the registering grooves, another of the sealing surfaces including another edge of the plate having an arcuate portion for sealing against a surface of another of the registering grooves.
In a further preferred embodiment according to the present invention, there is provided a method of locating a seal along registering faces of first and second mating parts of a gas turbine, comprising the steps of providing a first groove having a first depth in a registering face of the first part, providing a second groove having a second depth in a registering face of the second part, the depth of the first groove being in excess of the depth of the second groove, providing a seal having a depth equal to or less than the depth of the first groove and greater than the depth of the second groove, retaining the seal in the first groove during installation of the seal and releasing the seal from the first groove, enabling the seal to locate in the first and second grooves, spanning the joint between the mating parts.